US20210354977A1 - Microelectromechanical Device with Beam Structure over Silicon Nitride Undercut - Google Patents
Microelectromechanical Device with Beam Structure over Silicon Nitride Undercut Download PDFInfo
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- US20210354977A1 US20210354977A1 US17/320,188 US202117320188A US2021354977A1 US 20210354977 A1 US20210354977 A1 US 20210354977A1 US 202117320188 A US202117320188 A US 202117320188A US 2021354977 A1 US2021354977 A1 US 2021354977A1
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims abstract description 133
- 229910052581 Si3N4 Inorganic materials 0.000 title claims abstract description 116
- 239000000758 substrate Substances 0.000 claims abstract description 21
- 238000000034 method Methods 0.000 claims description 73
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 66
- 239000000463 material Substances 0.000 claims description 42
- 239000000377 silicon dioxide Substances 0.000 claims description 30
- 235000012239 silicon dioxide Nutrition 0.000 claims description 28
- 229910052721 tungsten Inorganic materials 0.000 claims description 15
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical group [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 12
- 239000010937 tungsten Substances 0.000 claims description 12
- 238000000151 deposition Methods 0.000 claims description 9
- 238000004519 manufacturing process Methods 0.000 claims description 8
- 239000011159 matrix material Substances 0.000 claims description 7
- 150000001875 compounds Chemical class 0.000 claims description 6
- 229910052741 iridium Inorganic materials 0.000 claims description 6
- 238000005498 polishing Methods 0.000 claims description 6
- 229910052719 titanium Inorganic materials 0.000 claims description 5
- 229910052697 platinum Inorganic materials 0.000 claims description 4
- 239000004065 semiconductor Substances 0.000 claims description 4
- 229910052715 tantalum Inorganic materials 0.000 claims description 4
- 229910010038 TiAl Inorganic materials 0.000 claims description 3
- 229910052737 gold Inorganic materials 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- 229910052763 palladium Inorganic materials 0.000 claims description 3
- 229910052709 silver Inorganic materials 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 229910052759 nickel Inorganic materials 0.000 claims description 2
- 238000000059 patterning Methods 0.000 claims description 2
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims 3
- 229910052718 tin Inorganic materials 0.000 claims 3
- 239000007769 metal material Substances 0.000 claims 2
- 229910019897 RuOx Inorganic materials 0.000 claims 1
- 229910004166 TaN Inorganic materials 0.000 claims 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims 1
- 229910052681 coesite Inorganic materials 0.000 claims 1
- 229910052593 corundum Inorganic materials 0.000 claims 1
- 229910052906 cristobalite Inorganic materials 0.000 claims 1
- VRIVJOXICYMTAG-IYEMJOQQSA-L iron(ii) gluconate Chemical compound [Fe+2].OC[C@@H](O)[C@@H](O)[C@H](O)[C@@H](O)C([O-])=O.OC[C@@H](O)[C@@H](O)[C@H](O)[C@@H](O)C([O-])=O VRIVJOXICYMTAG-IYEMJOQQSA-L 0.000 claims 1
- 229910052682 stishovite Inorganic materials 0.000 claims 1
- 229910052905 tridymite Inorganic materials 0.000 claims 1
- 238000007740 vapor deposition Methods 0.000 claims 1
- 229910001845 yogo sapphire Inorganic materials 0.000 claims 1
- 239000010410 layer Substances 0.000 description 121
- 230000008569 process Effects 0.000 description 60
- NRTOMJZYCJJWKI-UHFFFAOYSA-N Titanium nitride Chemical compound [Ti]#N NRTOMJZYCJJWKI-UHFFFAOYSA-N 0.000 description 24
- 235000012431 wafers Nutrition 0.000 description 23
- 229910052751 metal Inorganic materials 0.000 description 17
- 239000002184 metal Substances 0.000 description 17
- 238000005229 chemical vapour deposition Methods 0.000 description 16
- 239000010936 titanium Substances 0.000 description 12
- TXEYQDLBPFQVAA-UHFFFAOYSA-N tetrafluoromethane Chemical compound FC(F)(F)F TXEYQDLBPFQVAA-UHFFFAOYSA-N 0.000 description 9
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 8
- 150000002739 metals Chemical class 0.000 description 8
- 239000001301 oxygen Substances 0.000 description 8
- 229910052760 oxygen Inorganic materials 0.000 description 8
- 229910052710 silicon Inorganic materials 0.000 description 8
- 239000010703 silicon Substances 0.000 description 8
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 7
- 229910052782 aluminium Inorganic materials 0.000 description 7
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 7
- 239000003989 dielectric material Substances 0.000 description 7
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 7
- 230000004888 barrier function Effects 0.000 description 6
- 229910052799 carbon Inorganic materials 0.000 description 6
- 239000004020 conductor Substances 0.000 description 6
- 238000005530 etching Methods 0.000 description 6
- 229910000040 hydrogen fluoride Inorganic materials 0.000 description 6
- 230000035882 stress Effects 0.000 description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 5
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 description 5
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 5
- 239000011737 fluorine Substances 0.000 description 5
- 229910052731 fluorine Inorganic materials 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 238000002844 melting Methods 0.000 description 5
- KDLHZDBZIXYQEI-UHFFFAOYSA-N palladium Substances [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 5
- 229910017107 AlOx Inorganic materials 0.000 description 4
- -1 aluminum (Al) Chemical class 0.000 description 4
- 229910052750 molybdenum Inorganic materials 0.000 description 4
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- MZLGASXMSKOWSE-UHFFFAOYSA-N tantalum nitride Chemical compound [Ta]#N MZLGASXMSKOWSE-UHFFFAOYSA-N 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 239000010931 gold Substances 0.000 description 3
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 3
- 238000001465 metallisation Methods 0.000 description 3
- BPUBBGLMJRNUCC-UHFFFAOYSA-N oxygen(2-);tantalum(5+) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ta+5].[Ta+5] BPUBBGLMJRNUCC-UHFFFAOYSA-N 0.000 description 3
- 238000000623 plasma-assisted chemical vapour deposition Methods 0.000 description 3
- 230000001681 protective effect Effects 0.000 description 3
- 230000004044 response Effects 0.000 description 3
- WOCIAKWEIIZHES-UHFFFAOYSA-N ruthenium(iv) oxide Chemical compound O=[Ru]=O WOCIAKWEIIZHES-UHFFFAOYSA-N 0.000 description 3
- 238000004544 sputter deposition Methods 0.000 description 3
- PBCFLUZVCVVTBY-UHFFFAOYSA-N tantalum pentoxide Inorganic materials O=[Ta](=O)O[Ta](=O)=O PBCFLUZVCVVTBY-UHFFFAOYSA-N 0.000 description 3
- BLIQUJLAJXRXSG-UHFFFAOYSA-N 1-benzyl-3-(trifluoromethyl)pyrrolidin-1-ium-3-carboxylate Chemical compound C1C(C(=O)O)(C(F)(F)F)CCN1CC1=CC=CC=C1 BLIQUJLAJXRXSG-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 229910001030 Iron–nickel alloy Inorganic materials 0.000 description 2
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 2
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 2
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 2
- 229910001080 W alloy Inorganic materials 0.000 description 2
- 238000013459 approach Methods 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- HTXDPTMKBJXEOW-UHFFFAOYSA-N dioxoiridium Chemical compound O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 229910000457 iridium oxide Inorganic materials 0.000 description 2
- 239000011733 molybdenum Substances 0.000 description 2
- 239000010955 niobium Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000005240 physical vapour deposition Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 239000010948 rhodium Substances 0.000 description 2
- 229910052707 ruthenium Inorganic materials 0.000 description 2
- 229910001925 ruthenium oxide Inorganic materials 0.000 description 2
- 239000004332 silver Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 2
- 239000004408 titanium dioxide Substances 0.000 description 2
- 238000012876 topography Methods 0.000 description 2
- ZSLUVFAKFWKJRC-IGMARMGPSA-N 232Th Chemical compound [232Th] ZSLUVFAKFWKJRC-IGMARMGPSA-N 0.000 description 1
- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 description 1
- 229910001369 Brass Inorganic materials 0.000 description 1
- 229910000906 Bronze Inorganic materials 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 239000004593 Epoxy Substances 0.000 description 1
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910052765 Lutetium Inorganic materials 0.000 description 1
- 229910020294 Pb(Zr,Ti)O3 Inorganic materials 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 229910004158 TaO Inorganic materials 0.000 description 1
- 229910052776 Thorium Inorganic materials 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- KGWWEXORQXHJJQ-UHFFFAOYSA-N [Fe].[Co].[Ni] Chemical compound [Fe].[Co].[Ni] KGWWEXORQXHJJQ-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- UQZIWOQVLUASCR-UHFFFAOYSA-N alumane;titanium Chemical compound [AlH3].[Ti] UQZIWOQVLUASCR-UHFFFAOYSA-N 0.000 description 1
- LUKDNTKUBVKBMZ-UHFFFAOYSA-N aluminum scandium Chemical compound [Al].[Sc] LUKDNTKUBVKBMZ-UHFFFAOYSA-N 0.000 description 1
- CXOWYMLTGOFURZ-UHFFFAOYSA-N azanylidynechromium Chemical compound [Cr]#N CXOWYMLTGOFURZ-UHFFFAOYSA-N 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 239000010951 brass Substances 0.000 description 1
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- 239000003990 capacitor Substances 0.000 description 1
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- 229910052804 chromium Inorganic materials 0.000 description 1
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- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 239000000084 colloidal system Substances 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- KUNSUQLRTQLHQQ-UHFFFAOYSA-N copper tin Chemical compound [Cu].[Sn] KUNSUQLRTQLHQQ-UHFFFAOYSA-N 0.000 description 1
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
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- 230000006355 external stress Effects 0.000 description 1
- 150000002221 fluorine Chemical class 0.000 description 1
- 229910052735 hafnium Inorganic materials 0.000 description 1
- VBJZVLUMGGDVMO-UHFFFAOYSA-N hafnium atom Chemical compound [Hf] VBJZVLUMGGDVMO-UHFFFAOYSA-N 0.000 description 1
- KQHQLIAOAVMAOW-UHFFFAOYSA-N hafnium(4+) oxygen(2-) zirconium(4+) Chemical compound [O--].[O--].[O--].[O--].[Zr+4].[Hf+4] KQHQLIAOAVMAOW-UHFFFAOYSA-N 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 239000011229 interlayer Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 229910000464 lead oxide Inorganic materials 0.000 description 1
- HFGPZNIAWCZYJU-UHFFFAOYSA-N lead zirconate titanate Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ti+4].[Zr+4].[Pb+2] HFGPZNIAWCZYJU-UHFFFAOYSA-N 0.000 description 1
- 229910052451 lead zirconate titanate Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- OHSVLFRHMCKCQY-UHFFFAOYSA-N lutetium atom Chemical compound [Lu] OHSVLFRHMCKCQY-UHFFFAOYSA-N 0.000 description 1
- 238000003913 materials processing Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 230000005405 multipole Effects 0.000 description 1
- WIIZEEPFHXAUND-UHFFFAOYSA-N n-[[4-[2-(dimethylamino)ethoxy]phenyl]methyl]-3,4,5-trimethoxybenzamide;hydron;chloride Chemical compound Cl.COC1=C(OC)C(OC)=CC(C(=O)NCC=2C=CC(OCCN(C)C)=CC=2)=C1 WIIZEEPFHXAUND-UHFFFAOYSA-N 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 229910052762 osmium Inorganic materials 0.000 description 1
- SYQBFIAQOQZEGI-UHFFFAOYSA-N osmium atom Chemical compound [Os] SYQBFIAQOQZEGI-UHFFFAOYSA-N 0.000 description 1
- YEXPOXQUZXUXJW-UHFFFAOYSA-N oxolead Chemical compound [Pb]=O YEXPOXQUZXUXJW-UHFFFAOYSA-N 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 229910052702 rhenium Inorganic materials 0.000 description 1
- WUAPFZMCVAUBPE-UHFFFAOYSA-N rhenium atom Chemical compound [Re] WUAPFZMCVAUBPE-UHFFFAOYSA-N 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 125000006850 spacer group Chemical group 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 229910052713 technetium Inorganic materials 0.000 description 1
- GKLVYJBZJHMRIY-UHFFFAOYSA-N technetium atom Chemical compound [Tc] GKLVYJBZJHMRIY-UHFFFAOYSA-N 0.000 description 1
- MAKDTFFYCIMFQP-UHFFFAOYSA-N titanium tungsten Chemical compound [Ti].[W] MAKDTFFYCIMFQP-UHFFFAOYSA-N 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 235000012773 waffles Nutrition 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Images
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B3/00—Devices comprising flexible or deformable elements, e.g. comprising elastic tongues or membranes
- B81B3/0018—Structures acting upon the moving or flexible element for transforming energy into mechanical movement or vice versa, i.e. actuators, sensors, generators
- B81B3/0021—Transducers for transforming electrical into mechanical energy or vice versa
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
- B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
- B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
- B81C1/00134—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems comprising flexible or deformable structures
- B81C1/0015—Cantilevers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B3/00—Devices comprising flexible or deformable elements, e.g. comprising elastic tongues or membranes
- B81B3/0064—Constitution or structural means for improving or controlling the physical properties of a device
- B81B3/0086—Electrical characteristics, e.g. reducing driving voltage, improving resistance to peak voltage
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B2201/00—Specific applications of microelectromechanical systems
- B81B2201/01—Switches
- B81B2201/012—Switches characterised by the shape
- B81B2201/014—Switches characterised by the shape having a cantilever fixed on one side connected to one or more dimples
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B2203/00—Basic microelectromechanical structures
- B81B2203/01—Suspended structures, i.e. structures allowing a movement
- B81B2203/0118—Cantilevers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B2207/00—Microstructural systems or auxiliary parts thereof
- B81B2207/01—Microstructural systems or auxiliary parts thereof comprising a micromechanical device connected to control or processing electronics, i.e. Smart-MEMS
- B81B2207/015—Microstructural systems or auxiliary parts thereof comprising a micromechanical device connected to control or processing electronics, i.e. Smart-MEMS the micromechanical device and the control or processing electronics being integrated on the same substrate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B2207/00—Microstructural systems or auxiliary parts thereof
- B81B2207/09—Packages
- B81B2207/091—Arrangements for connecting external electrical signals to mechanical structures inside the package
- B81B2207/094—Feed-through, via
- B81B2207/096—Feed-through, via through the substrate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
- B81C2201/00—Manufacture or treatment of microstructural devices or systems
- B81C2201/01—Manufacture or treatment of microstructural devices or systems in or on a substrate
- B81C2201/0101—Shaping material; Structuring the bulk substrate or layers on the substrate; Film patterning
- B81C2201/0128—Processes for removing material
- B81C2201/013—Etching
- B81C2201/0132—Dry etching, i.e. plasma etching, barrel etching, reactive ion etching [RIE], sputter etching or ion milling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
- B81C2203/00—Forming microstructural systems
- B81C2203/07—Integrating an electronic processing unit with a micromechanical structure
- B81C2203/0707—Monolithic integration, i.e. the electronic processing unit is formed on or in the same substrate as the micromechanical structure
- B81C2203/0735—Post-CMOS, i.e. forming the micromechanical structure after the CMOS circuit
Definitions
- This relates to microelectromechanical devices that include a released mechanical structure positioned over an undercut in a silicon nitride layer.
- Microelectromechanical (MEM) relays can play an important role as a device for adding functionality and decreasing the power consumption for various applications such as sensors and consumable devices for the Internet of things (IoT) and wearables.
- MEMS device is a mechanical relay. These devices have the capability of a quasi-ideal switching behavior with a very abrupt on-off switching, and zero current leakage during the OFF-state. Multi-terminal operation of relays can also save energy. See, for example, Martin Riverolo, et al, “High Performance Seesaw Torsional CMOS-MEMS Relay Using Tungsten VIA Layer,” 2018.
- a complementary metal oxide semiconductor (CMOS) platform can be used for the monolithic fabrication of such MEMS relays in a combination with classical CMOS devices.
- CMOS complementary metal oxide semiconductor
- CMOS MEMS is a technology where Al (aluminum) metallization and chemical vapor deposition (CVD) of tungsten (W) in VIA masks are used to create MEMS structures.
- SiO 2 silicon dioxide
- the SiO 2 is typically removed using vapor hydrogen fluoride (HF) or liquid HF.
- HF vapor hydrogen fluoride
- Some CMOS MEMS devices use silicon (Si) (single crystal or polycrystal) as the MEMS removable layer.
- the Si can be etched with plasma fluorine (F) process or xenon difluoride (XeF2).
- a microelectromechanical system is located on a substrate.
- a silicon nitride (SiN) layer on a portion of the substrate.
- a mechanical structure has first and second ends. The first end is embedded in the SiN layer, and the second end is cantilevered from the SiN layer.
- FIG. 1 is a cross sectional view of a portion of an example CMOS integrated circuit chip that includes a MEMS device with a beam formed in a layer of silicon nitride.
- FIG. 2 is a top sectional view of the MEMS device of FIG. 1 .
- FIGS. 3A-3F illustrate fabrication steps for the MEMS device of FIGS. 1 and 2 .
- FIG. 4A is a top sectional view and FIG. 4B is a cross sectional view of another example CMOS integrated circuit chip that includes a MEMS device with a beam formed in a layer of silicon nitride.
- FIG. 5 is a cross sectional view of another example CMOS integrated circuit chip that includes a MEMS device with a beam formed in a layer of silicon nitride.
- FIG. 6 is an example packaged MEMS device.
- CMOS MEMS has several characteristics that makes it attractive. CMOS is quite mature, and analog or other circuits can be incorporated on the same wafer as a MEMS device(s). CMOS wafers are relatively inexpensive and can be fabricated with a wide variety of known process technologies.
- SiO2 silicon dioxide
- a dielectric layer of SiO2 is formed and then a metallic structure is formed on the layer of SiO2.
- a wet hydrofluoric (HF) etch that is typically is used to undercut a portion of the SiO2 to release a portion of the metallic structure to form a MEMS device creates a high stress that is limiting for MEMS structure.
- the HF etch also attacks some of the other materials, like titanium (Ti), that are typically used within CMOS structures.
- Vapor HF is even more reactive and attacks SiN, which is typically used as a dielectric material. This makes it difficult to create dielectric elements that are part of a MEMS structure.
- CMOS process also has a limitation in that it may not include materials that are needed for MEMS devices such as relays.
- Conductive materials that are used in a CMOS process such as W and titanium nitride (TiN) do not create good contacts for MEMS devices, such as relays.
- CMOS metals such as: aluminum (Al), Ti, TiN, titanium tungsten alloy (TiW), W, copper (Cu), tantalum (Ta), tantalum nitride (TaN)
- alternative materials such: as tantalum pentoxide (Ta2O5), titanium dioxide (TiO2), aluminum oxide (Al2O3), titanium aluminum nitride (TiAlN), chromium nitride (CrN), titanium aluminum oxide nitride (TiAlON), molybdenum (Mo), aluminum nitride (AlN), aluminum scandium nitride (AlScN), hafnium zirconium oxide (HfZrOx), platinum (Pt), iridium (Ir), Iridium oxide (IrOx), lead zirconate titanate (Pb(Zr,Ti)O3), lead (Pd), lead oxide (PdO), gold (Au),
- CMOS complementary metal-oxide-semiconductor
- CMP chemical mechanical polishing
- This process is similar to that used to ash resist. This plasma process etches the SiN in a mostly isotropic fashion. This is a useful characteristic for undercut etch of MEMS structures. This is a completely different etch process compared to VIA etch where a directional etch is needed to produce vias.
- SiO2 and many other dielectrics such as Al 2 O 3 , Ta2O5, TiO2 can be used to create a dielectric feature that is not strongly attacked by the plasma etch undercut process.
- FIG. 1 is a cross-sectional view of a portion of a CMOS integrated circuit chip that includes a MEMS device 100 with a beam 120 formed in a layer of silicon nitride 104 .
- FIG. 2 is top sectional view of the MEMS device of FIG. 1 .
- beam 120 is part of MEMS device 100 .
- This figure shows the illustration of a simple cantilever beam with two layers.
- the bottom layer is W 120 .
- This layer is formed using the typical W VIA damascene process flow.
- VIA pattern with a maximum space for each via but a mesh structure can be used to create large features.
- SiN etch which may or may not stop on another patterned layer is used to better define the thickness.
- Ti adhesion and barrier layer 105 that is typically CVD TiN (actually TiCON). These barrier materials can be other materials like Ta, TaN, Ru, etc.
- the trenches are then filled with CVD W and then W outside of the trenches is removed using CMP. The CMP or follow up clean removes the adhesion/barrier layer (Ti/TiN) 105 . Since the W needs to be protected from the SiN undercut etch it needs to be protected by materials that are not etched.
- One technique shown in this figure is to use layer 132 which in this example is Al on TiN.
- Example dielectric materials for 132 are AlOx, AlN, SiO2, TaO, TiO2.
- This layer can be patterned using another mask with etch processes. Another option is to make this a self-aligned protection layer. This process typically starts with a W recess etch (dry or wet) that removes W faster than SiN. A protective insulating or conductive barrier layer is then deposited and then CMP or an etchback process is used to remove the layer above the SiN. In this manner the W is protected without using an additional mask step. A key point is that these materials etch at a much slower rate than the SiN in the undercut etch process.
- a layer of SiN 104 is formed over a substrate 102 , which is this example is silicon (Si).
- substrate 102 silicon
- Si silicon
- a CMOS process typically fabricates active devices in a thin epitaxial layer of silicon that is formed on top of a bulk wafer of silicon.
- Beam 120 is significantly longer than it is thick.
- Typical VIA thicknesses 121 are those used in CMOS devices which are typically between 0.1 um to approximately Sum. The total beam thickness in this example is VIA thickness plus any additional layers above layer 132 or below layer 120 (not present in this figure).
- the released beam length 124 is typically much longer than it is wide with a typical aspect ratio (length to height) of 5 to 1 or even much larger. For example, if the beam is 1 um thick 121 , then the released portion 124 of beam 120 is typically much longer than Sum. In other examples, the released portion of such a beam can be longer than 20 um and potentially longer than even 100 um, depending on material and cross-section design.
- the total length 122 of cantilevered beam feature 120 is always longer than the released beam length 124 so that there is a reasonable length 125 still embedded in remaining SiN 104 .
- beam 120 is fabricated from tungsten (W) with a thin liner of TiN.
- the tungsten and TiN are deposited using a known chemical vapor deposition (CVD) technique in a damascene style process and CMP of the W and TiN are used to remove unwanted metal.
- the TiN also acts as diffusion barrier and also as an etch protection layer for the W after the SiN has been removed by the undercut etch process.
- a thin layer of Ti which is typically used as an adhesion layer and also used to create a lower resistance electrical connection to metals below this structure.
- the Ti is typically deposited with directional sputter deposition using ionized metal plasma in order to achieve thin layer of metal on the bottom of the VIA type feature.
- Damascene is the art of encrusting gold, silver, or copper wire on the surface of iron, steel, bronze, or brass.
- a narrow undercut is made in the surface of the metal with a chisel and the wire forced into the undercut by means of a hammer.
- CMOS process a CMP process is used to remove unwanted tungsten after the CVD process, as described in more detail herein below. This requires a flat surface, so either the surface is un-patterned, or CMP has been used to make it flat prior to the W pattern step. While this is similar to what is done in a CMOS process, in this case the W is surrounded on the bottom and sides by a SiN layer 103 rather than SiO2.
- a dielectric layer is first deposited onto the substrate.
- the dielectric layer is then patterned and filled by metal deposition.
- a dual-damascene process is characterized by patterning vias and trenches in such a way that the metal deposition fills both at the same time while leaving interstitial regions between the vias and trenches.
- the damascene process for beam 120 uses existent interlayer dielectrics in which the vias and trenches for conduction paths are etched.
- the dielectric layer 103 is SiN and the metal for beam 120 is tungsten.
- the metal for beam 120 may be selected from other metals, such as TiW.
- W or TiW is used to create the MEMS beam structure 120 and provides a low creep rate.
- Creep in this instance is the change in deflection of the beam after being subjected to time and temperature and possibly added stress.
- Typical product times/temperatures are 10 yr, 85 C, 105 C, 125 C or 150 C. Some products require longer times or even higher temperatures.
- the stress depends on the application. There is always built in internal stress that might cause the beam to change position even without the added external stress. Many devices require that the beam position (lateral and vertical) not change when not under outside stress. Of course, beams always have a spring constant and do bend under stress.
- the thickness of the W is selected to provide greater than approximately 75% of the stiffness for beam 120 so a slow creep of other materials does not degrade the properties of the overall MEMS structure.
- a thin layer 105 of TiN surrounds beam 120 , and an aluminum conductor 132 is patterned on top of beam 120 .
- Aluminum is known to have a high creep rate but the overall beam or MEMS structure will not move much if the W has little relative creep and is a dominant fraction of the beams stiffness.
- the Al layer can be used not only to protect the top of the W in the beam from the SiN undercut etch but also as an electrical contact to the beam.
- the Al layer can also be on the bottom of the beam and act as an etch stop for the beam.
- this Al layer also typically includes other materials like Ti, TiAl, TiN. In various examples, other materials may be present as needed for specific functionality.
- a sacrificial SiN layer 134 is formed on over SiN layer 104 and various other elements such as Al conductor 132 .
- An SiO2 dielectric layer 136 is formed on top of the SiN layer 134 . Opening 138 is patterned in dielectric layer 136 to guide an undercut process.
- the layer 136 can be multiple layers or even other materials than SiO2, such as AlOx, SiON.
- Undercut region 140 is formed using carbon tetrafluoride plus oxygen (CF4+O2) to provide a strong etch rate for SiN while only weakly etching SiO2 etch stop layer 103 and SiO2 top dielectric layer 136 .
- CF4+O2 carbon tetrafluoride plus oxygen
- this process needs plasma activated fluorine plus oxygen.
- F such as SF6 or other fluorocarbons, plus F2, NF3, HF, etc.
- the listing of CF4+O2 is a common process that has demonstrated good results but other processes with these alternate chemistries do exist. As illustrated in FIGS.
- a portion 141 of undercut region 140 extends across the bottom of a released portion 124 of beam 120 and up the sides of portion 124 of beam 120 .
- a portion 142 of SiN layer 134 is also etched away. Regions 140 , 141 , 142 together are a cavity region in SiN layer 104 , 134 into which a portion of beam 120 is cantilevered. In this manner, the cantilevered released portion 124 of beam 120 is separated from SiN layers 104 , 134 and can therefore move in response to a force, such as an electrostatic force.
- Another portion 125 of beam 120 remains firmly embedded and anchored in SiN layer 104 . In this manner the beam 120 can function as part of MEMS device 100 .
- FIGS. 3A-3F illustrate fabrication steps for MEMS device 100 of FIGS. 1 and 2 .
- An entire wafer 300 that contains tens or hundreds of devices is fabricated as one unit. For simplicity, only a small upper portion of substrate 302 of the wafer 300 is illustrated.
- a layer 303 of SiO2 is formed over a substrate 302 , which is this example is silicon (Si).
- a CMOS process typically fabricates active devices in a thin epitaxial layer of silicon that is formed on top of a bulk wafer of silicon.
- SiO2 layer 303 will act as an etch stop during an undercut process.
- a layer of SiN 304 is then formed over the SiO2 303 layer.
- SiN layer 304 is thick enough to allow beam 120 ( FIG. 2 ) to be formed within it.
- SiN layer 304 One or more deposition steps may be required to achieve a sufficient thickness of SiN layer 304 .
- the generic term “SiN” for silicon nitride is used herein to refer to any of the various forms of silicon nitride, such as Si3N4, Si(x)N(y)H(z), etc.
- the SiN layer has a composition of SiOxNyCz where O is less than 0.1 and C is less than 0.3 and the N makes up the remaining fraction of the material excluding the Si.
- the hydrogen (H) symbol is typically omitted from the chemical formulas, such as SiN, but is frequently present in many of these materials including metals.
- SiN layer 104 is deposited using a chemical vapor deposition (CVD) process or plasma enhanced chemical vapor deposition (PECVD).
- Chemical vapor deposition is a coating process that uses thermally induced chemical reactions at the surface of a heated substrate, with reagents supplied in gaseous form.
- the most common CVD or PECVD silicon nitride typically contains up to 8% hydrogen.
- Other methods to deposit SiN is sputter deposition or electron evaporation, but this is less common.
- the wafer surface is typically flattened using a chemical mechanical polishing (CMP) process.
- CMP chemical mechanical polishing
- the CMP process uses an abrasive and corrosive chemical slurry (commonly a colloid) in conjunction with a polishing pad and retaining ring, typically of a greater diameter than the wafer.
- the pad and wafer are pressed together by a dynamic polishing head and held in place by a retaining ring.
- the dynamic polishing head is rotated with different axes of rotation (i.e., not concentric). This removes material and tends to even out any irregular topography, making the top surface 3041 of the wafer flat, also referred to as “planar”.
- surface 3041 is patterned and etched using a known or later developed etching technique to form trench 306 within SiN layer 304 .
- a thin layer 305 if TiN is then deposited over the wafer. The TiN layer coats the floor and wall of trench 306 .
- a layer 307 of tungsten is deposited over the surface of the wafer and into cavity 306 .
- Tungsten layer 307 adheres to TiN layer 305 .
- FIG. 3D another CMP step has been performed to remove tungsten layer 307 everywhere except within trench 306 .
- beam 320 is formed within SiN layer 304 .
- this is a damascene style process.
- An alternative to using CMP to remove these layers is an etch-back process.
- TiN layer 330 is deposited over the surface of wafer 300 .
- a layer of aluminum is then deposited over the surface of wafer 300 .
- a sacrificial layer (not shown) is then deposited, patterned, and etched to form aluminum conductor 332 that forms a contact for MEMS relay device 100 ( FIG. 1 ).
- Another layer 334 of SiN is then deposited over the surface of wafer 300 , followed by a CMP process to planarize the surface 3042 of wafer 300 .
- a SiO2 dielectric layer 336 is deposited over the planarized surface of wafer 300 .
- a sacrificial layer (not shown) is then deposited, patterned, and etched to form openings 338 and 339 .
- Opening 338 will guide the undercut process around beam 320 .
- Opening 339 will guide an etch process to form a via to contact to aluminum conductor 332 . While only two openings are illustrated for simplicity, other openings are made for various contact points to other features (not shown) on wafer 300 .
- wafer 300 is exposed to a carbon tetrafluoride plus oxygen (CF4+O2) plasma 350 , 351 through openings 338 , 339 to provide a strong etch rate for SiN layers 304 , 334 while only weakly etching SiO2 etch stop layer 303 and SiO2 top dielectric layer 336 .
- CF4+O2 carbon tetrafluoride plus oxygen
- undercut region 340 and contact region 343 are formed.
- a portion 341 of undercut region 340 extends across the bottom of a released portion 324 of beam 320 and up the sides of the portion 324 of beam 320 .
- a portion 342 of SiN layer 334 is also etched away.
- Regions 340 , 341 , 342 together are a cavity region in SiN layer 304 , 334 into which a portion of beam 320 is cantilevered. Released portion 324 of beam 320 is separated from SiN layers 304 , 334 to form a released mechanical structure and can therefore move in response to a force, such as an electrostatic force. Another portion 325 of beam 320 remains firmly anchored in SiN layer 304 . In this manner, beam 320 can function as part of a resonator or a support beam in a MEMS relay, for example.
- CMOS transistors may also be fabricated on wafer 300 using known or later developed integrated circuit fabrication techniques. Upon completion, wafer 300 is sawn, or otherwise separated, into individual chips, also known as die. The separate die are then attached to a lead frame and encapsulated using a known or later developed IC packaging technique, such as molding with a mold compound, to provide a packaged MEMS device integrated with CMOS circuitry.
- a known or later developed IC packaging technique such as molding with a mold compound
- FIG. 4A is a top sectional view and FIG. 4B is a cross sectional view of a portion of another example CMOS integrated circuit chip that includes a MEMS device 400 with a beam 420 formed in a layer(s) 404 , 434 of silicon nitride.
- beam 420 is fabricated with a matrix of vias and troughs, as indicated in general at 427 , etched through a portion 424 of beam 420 .
- the matrix of vias and troughs 427 result in a matrix of interconnected metallic members 427 with interstitial space 426 distributed throughout beam portion 424 .
- interstitial space 426 will be filled with SiN from SiN remaining from SiN layer 404 .
- interconnected metallic members 427 of beam portion 424 resemble a waffle pattern.
- MEMS device 400 is fabricated in a similar manner as shown in FIGS. 3A-3F with the added steps of fabricating vias 426 and troughs 427 .
- a wafer on which MEMS device 400 is fabricated is exposed to a carbon tetrafluoride plus oxygen (CF4+O2) plasma 450 , 451 through openings 438 , 439 to provide a strong etch rate for SiN layers 404 , 434 while only weakly etching SiO2 etch stop layer 403 on substrate 402 and SiO2 top dielectric layer 436 .
- CF4+O2 carbon tetrafluoride plus oxygen
- undercut region 440 and contact region 443 are formed.
- a portion 441 of undercut region 440 extends across the bottom of a portion 424 of beam 420 and up the sides of the portion 424 of beam 420 .
- a portion 442 of SiN layer 434 is also etched away so that portion 424 of beam 420 is separated from SiN layers 404 , 434 to form a released mechanical structure and can therefore move in response to a force, such as an electrostatic force.
- Another portion 425 of beam 420 remains firmly anchored in SiN layer 404 . In this manner, beam 420 can function as a MEMS relay.
- plasma etch 450 removes SiN from interstitial space 426 and then diffuses through interstitial space 426 to form portions of undercut region 441 .
- an extensive undercut region 441 can be formed under beams that are larger than a what can be formed under a solid beam, such as beam 120 ( FIG. 1 ).
- FIG. 5 is a cross sectional view of a portion of another example CMOS integrated circuit chip that includes a MEMS device 500 with a released mechanical structure 520 formed in a layer(s) of silicon nitride 504 , 534 on a silicon substrate 502
- the W VIA feature 520 surrounded by CVD TiN 505 on all sides but the top, originally embedded in SiN lands on a patterned metal feature.
- the bottom patterned feature contains layer of 560 of iridium (Ir) is positioned on the bottom of beam 520 during the fabrication process.
- the bottom patterned feature can be made of any material dielectric or metallic that is not strongly attacked by the SiN undercut etch.
- the bottom layer is composed of a layer of 561 TiAlN on top of Ir 560 .
- the Ir 560 is on the bottom of a moving MEMS beam 520 .
- the W is protected from the SiN undercut etch process by SiO2 536 on top of the W.
- the CVD TiN can protect the W on the sides and on the bottom if necessary. In this case this protective top layer is patterned and etched prior to the SiN undercut process.
- undercut region 540 is fabricated using a plasma of carbon, fluorine, and oxygen (CxFy+O2) to provide selective gas removal of the SiN layers 503 , 534 through an opening in dielectric SiO2 layer 536 and yet not attack the Ir layer 560 or etch stop SiO2 layer 503 .
- CxFy+O2 a plasma of carbon, fluorine, and oxygen
- FIG. 6 is an example packaged MEMS device 600 .
- an integrated circuit chip 671 is fabricated using a known or later developed CMOS fabrication technique.
- CMOS circuitry 672 is formed in IC 671 and includes CMOS transistors, passive devices, and interconnecting conductors.
- One or more MEMS device 673 is formed in IC 671 .
- MEMS device 673 may be similar to any of devices 100 ( FIG. 1 ), 400 ( FIGS. 4A, 4B ), 500 ( FIG. 5 ) or other MEMS device fabricated within a SiN layer using a plasma etch process as described in more detail hereinabove.
- IC 671 is attached to a lead frame 670 that includes contacts 674 .
- Bond wires 675 connect bond pads on IC 671 to contacts 674 using a known or later developed wire bonding technique.
- a mold compound 676 encapsulates IC 671 using a known or later developed encapsulation technique.
- completed MEMS device 600 is packaged as a surface mount device.
- CVD tungsten protected by CVD TiN on 3 sides is used to form a beam structure within SiN.
- the top side can be protected by another patterned and etched layer or by a self-aligned process like recess the W followed by barrier metal like TiN and more CMP.
- PVD physical vapor deposition
- TiN, TiW, TiN, TaN may be used to form a beam structure within SiN, for example.
- the use of a carbon, fluorine, and oxygen plasma to undercut the SiN has less impact on other materials.
- SiN is stronger and has a higher thermal conductivity than SiO2.
- SiN undercut etch results in a clean surface where residual carbon or fluorine can be removed using plasma or vapor cleaning process with H2, H2O, O2, N2, NH3, NO, etc.
- W is used for the low creep material.
- low creep materials examples of which are included in Table 1. All the materials in Table 1 have extremely high melting temperatures above 1500 C, with most of them having a melting temperature above 2000 C. Materials that are typically used in semiconductor processing that qualify as low creep materials are C, Ta, Mo, Ir, Ru, Ti, and Pd. In addition, there are compounds like TiN or TaN that also qualify as high melting point and low creep materials. Alloys including the commonly used W alloys like TiW and NiW are also high melting temperature and low creep. With a few exceptions, most of the materials listed in Table Tare not typically used in CMOS processing and therefore do not have a well-established materials processing infrastructure of deposition, etch and clean.
- a simple beam structure that can be used as a relay is described.
- a beam that has a generally rectangular shape is described.
- more complex structures may be formed within SiN using the plasma etch process described herein.
- These structures can be used in an extremely wide variety of different MEMS structures.
- a wide variety of materials that are compatible with the plasma etch undercut process can be used to create many types of possible devices.
- These can be simple structures to create actuators using electrostatic, magnetic, piezoelectric, thermal.
- the high temperature metals such as Pt, Ir, W, Ru, Mo, Ti can be used to create high temperature heaters which have numerous applications such as gas flow sensors, IR sources.
- MEMS structures with these can be used to create resonators, IR detectors, heat detectors.
- Electrical structures such as relays or RF switches with reliable contact materials are possible.
- Variable capacitor devices can be made using a flexible beam as described herein.
- a portion of a beam is released from a SiN layer, while another portion remains embedded in the SiN layer.
- a released mechanical structure that has no portion remaining in the SiN layer may be fabricated.
- a released mechanical structure may be supported by a torsion bar or similar support mechanism that is attached to the SiN layer.
- the term “mechanical structure” refers to both fully and partially released structures of various shapes and sizes.
- a cantilevered beam is positioned within a cavity in a SiN layer.
- the SiN layer may be configured so that it does not completely enclose the cantilevered mechanical structure. For example, there may not be a top layer over the mechanical structure. In another example, a large portion of the SiN layer may be removed, in which case the cantilevered mechanical structure may project from an edge of the SiN layer into essentially open space.
- the finished packaged devices are surface mount devices with multiple contacts on a bottom side of the package.
- the IC package may have any number of known or later developed configurations, and may have various form(s), material(s), shape(s), dimension(s), number(s) of contacts, shape(s) of contacts, etc.
- the MEMS resonator(s) and/or any other components may be packaged, mounted, etc. in the IC package in various configurations.
- Other examples of IC packages include a wafer-level package and a die-level package.
- DIP dual inline package
- Couple and derivatives thereof mean an indirect, direct, optical, and/or wireless electrical connection.
- that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through an optical electrical connection, and/or through a wireless electrical connection.
Abstract
Description
- This application claims priority to U.S. Provisional Patent Application No. 63/024,850 filed May 14, 2020, the entirety of which is incorporated herein by reference.
- This relates to microelectromechanical devices that include a released mechanical structure positioned over an undercut in a silicon nitride layer.
- Microelectromechanical (MEM) relays can play an important role as a device for adding functionality and decreasing the power consumption for various applications such as sensors and consumable devices for the Internet of things (IoT) and wearables. One type of MEMS device is a mechanical relay. These devices have the capability of a quasi-ideal switching behavior with a very abrupt on-off switching, and zero current leakage during the OFF-state. Multi-terminal operation of relays can also save energy. See, for example, Martin Riverolo, et al, “High Performance Seesaw Torsional CMOS-MEMS Relay Using Tungsten VIA Layer,” 2018. A complementary metal oxide semiconductor (CMOS) platform can be used for the monolithic fabrication of such MEMS relays in a combination with classical CMOS devices.
- CMOS MEMS is a technology where Al (aluminum) metallization and chemical vapor deposition (CVD) of tungsten (W) in VIA masks are used to create MEMS structures. One characteristic of this approach is that silicon dioxide (SiO2) between metal layers is used as the removable spacer. The SiO2 is typically removed using vapor hydrogen fluoride (HF) or liquid HF. Some CMOS MEMS devices use silicon (Si) (single crystal or polycrystal) as the MEMS removable layer. The Si can be etched with plasma fluorine (F) process or xenon difluoride (XeF2).
- In described examples, a microelectromechanical system (MEMS) is located on a substrate. There is a silicon nitride (SiN) layer on a portion of the substrate. A mechanical structure has first and second ends. The first end is embedded in the SiN layer, and the second end is cantilevered from the SiN layer.
-
FIG. 1 is a cross sectional view of a portion of an example CMOS integrated circuit chip that includes a MEMS device with a beam formed in a layer of silicon nitride. -
FIG. 2 is a top sectional view of the MEMS device ofFIG. 1 . -
FIGS. 3A-3F illustrate fabrication steps for the MEMS device ofFIGS. 1 and 2 . -
FIG. 4A is a top sectional view andFIG. 4B is a cross sectional view of another example CMOS integrated circuit chip that includes a MEMS device with a beam formed in a layer of silicon nitride. -
FIG. 5 is a cross sectional view of another example CMOS integrated circuit chip that includes a MEMS device with a beam formed in a layer of silicon nitride. -
FIG. 6 is an example packaged MEMS device. - In the drawings, like elements are denoted by like reference numerals for consistency.
- CMOS MEMS has several characteristics that makes it attractive. CMOS is quite mature, and analog or other circuits can be incorporated on the same wafer as a MEMS device(s). CMOS wafers are relatively inexpensive and can be fabricated with a wide variety of known process technologies.
- An issue with fabricating MEMS using an example CMOS process is the silicon dioxide (SiO2) undercut process. Usually, a dielectric layer of SiO2 is formed and then a metallic structure is formed on the layer of SiO2. A wet hydrofluoric (HF) etch that is typically is used to undercut a portion of the SiO2 to release a portion of the metallic structure to form a MEMS device creates a high stress that is limiting for MEMS structure. The HF etch also attacks some of the other materials, like titanium (Ti), that are typically used within CMOS structures. Vapor HF is even more reactive and attacks SiN, which is typically used as a dielectric material. This makes it difficult to create dielectric elements that are part of a MEMS structure.
- An example CMOS process also has a limitation in that it may not include materials that are needed for MEMS devices such as relays. Conductive materials that are used in a CMOS process such as W and titanium nitride (TiN) do not create good contacts for MEMS devices, such as relays.
- In described examples, CMOS metals (such as: aluminum (Al), Ti, TiN, titanium tungsten alloy (TiW), W, copper (Cu), tantalum (Ta), tantalum nitride (TaN)) may be combined with alternative materials such: as tantalum pentoxide (Ta2O5), titanium dioxide (TiO2), aluminum oxide (Al2O3), titanium aluminum nitride (TiAlN), chromium nitride (CrN), titanium aluminum oxide nitride (TiAlON), molybdenum (Mo), aluminum nitride (AlN), aluminum scandium nitride (AlScN), hafnium zirconium oxide (HfZrOx), platinum (Pt), iridium (Ir), Iridium oxide (IrOx), lead zirconate titanate (Pb(Zr,Ti)O3), lead (Pd), lead oxide (PdO), gold (Au), silver (Ag), nickel iron alloy (NiFe), iron (Fe), cobalt (Co), nickel (Ni), cobalt nickel iron alloys (CoNiFe), ruthenium (Ru), ruthenium oxide (RuO2), etc. which may be useful for creating piezoelectric actuation and/or relay contacts with undercut SiN dielectric.
- These alternative materials can be included in a CMOS process by using SiN dielectric layers that are flattened using chemical mechanical polishing (CMP) steps during the fabrication process. This makes it possible to create CMOS using SiN as the dielectric between layers. A plasma process using carbon, fluorine, and oxygen (CxFy+O2) is used to provide selective gas removal of the SiN and yet not attack most of these metals and dielectrics. For example, a plasma carbon tetrafluoride plus oxygen (CF4+O2) provides a strong etch rate for SiN while only weakly etching SiO2. This selectivity applies to most of the other materials although there is some attack of W, Mo, and Ru or RuO2. A downstream plasma with a low substrate bias is used. This process is similar to that used to ash resist. This plasma process etches the SiN in a mostly isotropic fashion. This is a useful characteristic for undercut etch of MEMS structures. This is a completely different etch process compared to VIA etch where a directional etch is needed to produce vias.
- In described examples, SiO2 and many other dielectrics such as Al2O3, Ta2O5, TiO2 can be used to create a dielectric feature that is not strongly attacked by the plasma etch undercut process.
-
FIG. 1 is a cross-sectional view of a portion of a CMOS integrated circuit chip that includes aMEMS device 100 with abeam 120 formed in a layer ofsilicon nitride 104.FIG. 2 is top sectional view of the MEMS device ofFIG. 1 . In this example,beam 120 is part ofMEMS device 100. This figure shows the illustration of a simple cantilever beam with two layers. The bottom layer isW 120. This layer is formed using the typical W VIA damascene process flow. VIA pattern with a maximum space for each via but a mesh structure can be used to create large features. SiN etch which may or may not stop on another patterned layer is used to better define the thickness. The trenches are then etched and cleaned to remove resist that is left and any residue that might be present. The next step is depositing a Ti adhesion andbarrier layer 105 that is typically CVD TiN (actually TiCON). These barrier materials can be other materials like Ta, TaN, Ru, etc. The trenches are then filled with CVD W and then W outside of the trenches is removed using CMP. The CMP or follow up clean removes the adhesion/barrier layer (Ti/TiN) 105. Since the W needs to be protected from the SiN undercut etch it needs to be protected by materials that are not etched. One technique shown in this figure is to uselayer 132 which in this example is Al on TiN. In practice this can be other metals or dielectric materials that are not quickly attacked by the SiN undercut etch process. Example dielectric materials for 132 are AlOx, AlN, SiO2, TaO, TiO2. This layer can be patterned using another mask with etch processes. Another option is to make this a self-aligned protection layer. This process typically starts with a W recess etch (dry or wet) that removes W faster than SiN. A protective insulating or conductive barrier layer is then deposited and then CMP or an etchback process is used to remove the layer above the SiN. In this manner the W is protected without using an additional mask step. A key point is that these materials etch at a much slower rate than the SiN in the undercut etch process. - While this figure shows the creation of a cantilever, in practice multiple patterned and un-patterned layers can be below or above the MEMS layers that have been created using the undercut process. These additional layers may be used to create a wide variety of MEMS devices that can be created using this approach.
- In this example, a layer of
SiN 104 is formed over asubstrate 102, which is this example is silicon (Si). For simplicity, only a small upper portion ofsubstrate 102 is illustrated. As is known, a CMOS process typically fabricates active devices in a thin epitaxial layer of silicon that is formed on top of a bulk wafer of silicon. Also, for simplicity, this example is not drawn to scale.Beam 120 is significantly longer than it is thick. Typical VIA thicknesses 121 are those used in CMOS devices which are typically between 0.1 um to approximately Sum. The total beam thickness in this example is VIA thickness plus any additional layers abovelayer 132 or below layer 120 (not present in this figure). The releasedbeam length 124 is typically much longer than it is wide with a typical aspect ratio (length to height) of 5 to 1 or even much larger. For example, if the beam is 1 um thick 121, then the releasedportion 124 ofbeam 120 is typically much longer than Sum. In other examples, the released portion of such a beam can be longer than 20 um and potentially longer than even 100 um, depending on material and cross-section design. Thetotal length 122 ofcantilevered beam feature 120 is always longer than the releasedbeam length 124 so that there is areasonable length 125 still embedded in remainingSiN 104. - In this example,
beam 120 is fabricated from tungsten (W) with a thin liner of TiN. The tungsten and TiN are deposited using a known chemical vapor deposition (CVD) technique in a damascene style process and CMP of the W and TiN are used to remove unwanted metal. The TiN also acts as diffusion barrier and also as an etch protection layer for the W after the SiN has been removed by the undercut etch process. Not shown is a thin layer of Ti which is typically used as an adhesion layer and also used to create a lower resistance electrical connection to metals below this structure. The Ti is typically deposited with directional sputter deposition using ionized metal plasma in order to achieve thin layer of metal on the bottom of the VIA type feature. Damascene is the art of encrusting gold, silver, or copper wire on the surface of iron, steel, bronze, or brass. A narrow undercut is made in the surface of the metal with a chisel and the wire forced into the undercut by means of a hammer. In this example CMOS process, a CMP process is used to remove unwanted tungsten after the CVD process, as described in more detail herein below. This requires a flat surface, so either the surface is un-patterned, or CMP has been used to make it flat prior to the W pattern step. While this is similar to what is done in a CMOS process, in this case the W is surrounded on the bottom and sides by aSiN layer 103 rather than SiO2. - In a damascene process, a dielectric layer is first deposited onto the substrate. The dielectric layer is then patterned and filled by metal deposition. A dual-damascene process is characterized by patterning vias and trenches in such a way that the metal deposition fills both at the same time while leaving interstitial regions between the vias and trenches. The damascene process for
beam 120 uses existent interlayer dielectrics in which the vias and trenches for conduction paths are etched. In this case, thedielectric layer 103 is SiN and the metal forbeam 120 is tungsten. In another example, the metal forbeam 120 may be selected from other metals, such as TiW. - In this example, W or TiW is used to create the
MEMS beam structure 120 and provides a low creep rate. Creep in this instance is the change in deflection of the beam after being subjected to time and temperature and possibly added stress. Typical product times/temperatures are 10 yr, 85C, 105C, 125C or 150C. Some products require longer times or even higher temperatures. The stress depends on the application. There is always built in internal stress that might cause the beam to change position even without the added external stress. Many devices require that the beam position (lateral and vertical) not change when not under outside stress. Of course, beams always have a spring constant and do bend under stress. The thickness of the W is selected to provide greater than approximately 75% of the stiffness forbeam 120 so a slow creep of other materials does not degrade the properties of the overall MEMS structure. In the example shown, athin layer 105 of TiN surroundsbeam 120, and analuminum conductor 132 is patterned on top ofbeam 120. Aluminum is known to have a high creep rate but the overall beam or MEMS structure will not move much if the W has little relative creep and is a dominant fraction of the beams stiffness. In this example, the Al layer can be used not only to protect the top of the W in the beam from the SiN undercut etch but also as an electrical contact to the beam. The Al layer can also be on the bottom of the beam and act as an etch stop for the beam. In various examples, this Al layer also typically includes other materials like Ti, TiAl, TiN. In various examples, other materials may be present as needed for specific functionality. - A
sacrificial SiN layer 134 is formed on overSiN layer 104 and various other elements such asAl conductor 132. AnSiO2 dielectric layer 136 is formed on top of theSiN layer 134.Opening 138 is patterned indielectric layer 136 to guide an undercut process. Thelayer 136 can be multiple layers or even other materials than SiO2, such as AlOx, SiON. -
Undercut region 140 is formed using carbon tetrafluoride plus oxygen (CF4+O2) to provide a strong etch rate for SiN while only weakly etching SiO2etch stop layer 103 and SiO2 topdielectric layer 136. In practice this process needs plasma activated fluorine plus oxygen. There are multiple options for F such as SF6 or other fluorocarbons, plus F2, NF3, HF, etc. For O2 sources there are also multipole options such as H2O, O3, NO2, CO2, etc. The listing of CF4+O2 is a common process that has demonstrated good results but other processes with these alternate chemistries do exist. As illustrated inFIGS. 1 and 2 , aportion 141 of undercutregion 140 extends across the bottom of a releasedportion 124 ofbeam 120 and up the sides ofportion 124 ofbeam 120. Aportion 142 ofSiN layer 134 is also etched away.Regions SiN layer beam 120 is cantilevered. In this manner, the cantilevered releasedportion 124 ofbeam 120 is separated fromSiN layers portion 125 ofbeam 120 remains firmly embedded and anchored inSiN layer 104. In this manner thebeam 120 can function as part ofMEMS device 100. -
FIGS. 3A-3F illustrate fabrication steps forMEMS device 100 ofFIGS. 1 and 2 . Anentire wafer 300 that contains tens or hundreds of devices is fabricated as one unit. For simplicity, only a small upper portion ofsubstrate 302 of thewafer 300 is illustrated. - At
FIG. 3A , in this example, alayer 303 of SiO2 is formed over asubstrate 302, which is this example is silicon (Si). in this example, a CMOS process typically fabricates active devices in a thin epitaxial layer of silicon that is formed on top of a bulk wafer of silicon.SiO2 layer 303 will act as an etch stop during an undercut process. A layer ofSiN 304 is then formed over theSiO2 303 layer.SiN layer 304 is thick enough to allow beam 120 (FIG. 2 ) to be formed within it. - One or more deposition steps may be required to achieve a sufficient thickness of
SiN layer 304. The generic term “SiN” for silicon nitride is used herein to refer to any of the various forms of silicon nitride, such as Si3N4, Si(x)N(y)H(z), etc. In this example, the SiN layer has a composition of SiOxNyCz where O is less than 0.1 and C is less than 0.3 and the N makes up the remaining fraction of the material excluding the Si. The hydrogen (H) symbol is typically omitted from the chemical formulas, such as SiN, but is frequently present in many of these materials including metals. - In this example,
SiN layer 104 is deposited using a chemical vapor deposition (CVD) process or plasma enhanced chemical vapor deposition (PECVD). Chemical vapor deposition is a coating process that uses thermally induced chemical reactions at the surface of a heated substrate, with reagents supplied in gaseous form. The most common CVD or PECVD silicon nitride typically contains up to 8% hydrogen. Other methods to deposit SiN is sputter deposition or electron evaporation, but this is less common. - After deposition of
SiN layer 304 is complete, the wafer surface is typically flattened using a chemical mechanical polishing (CMP) process. This is necessary if there are layers underneath that have introduced topography. The CMP process uses an abrasive and corrosive chemical slurry (commonly a colloid) in conjunction with a polishing pad and retaining ring, typically of a greater diameter than the wafer. The pad and wafer are pressed together by a dynamic polishing head and held in place by a retaining ring. The dynamic polishing head is rotated with different axes of rotation (i.e., not concentric). This removes material and tends to even out any irregular topography, making thetop surface 3041 of the wafer flat, also referred to as “planar”. - At
FIG. 3B ,surface 3041 is patterned and etched using a known or later developed etching technique to formtrench 306 withinSiN layer 304. Athin layer 305 if TiN is then deposited over the wafer. The TiN layer coats the floor and wall oftrench 306. - At
FIG. 3C , alayer 307 of tungsten is deposited over the surface of the wafer and intocavity 306.Tungsten layer 307 adheres toTiN layer 305. - At
FIG. 3D , another CMP step has been performed to removetungsten layer 307 everywhere except withintrench 306. In this manner,beam 320 is formed withinSiN layer 304. As mentioned above, this is a damascene style process. An alternative to using CMP to remove these layers is an etch-back process. -
TiN layer 330 is deposited over the surface ofwafer 300. A layer of aluminum is then deposited over the surface ofwafer 300. A sacrificial layer (not shown) is then deposited, patterned, and etched to formaluminum conductor 332 that forms a contact for MEMS relay device 100 (FIG. 1 ). - Another
layer 334 of SiN is then deposited over the surface ofwafer 300, followed by a CMP process to planarize thesurface 3042 ofwafer 300. - At
FIG. 3E , aSiO2 dielectric layer 336 is deposited over the planarized surface ofwafer 300. A sacrificial layer (not shown) is then deposited, patterned, and etched to formopenings beam 320. Opening 339 will guide an etch process to form a via to contact toaluminum conductor 332. While only two openings are illustrated for simplicity, other openings are made for various contact points to other features (not shown) onwafer 300. - At
FIG. 3F ,wafer 300 is exposed to a carbon tetrafluoride plus oxygen (CF4+O2)plasma openings SiN layers etch stop layer 303 and SiO2 topdielectric layer 336. In this manner, undercutregion 340 andcontact region 343 are formed. Aportion 341 of undercutregion 340 extends across the bottom of a releasedportion 324 ofbeam 320 and up the sides of theportion 324 ofbeam 320. Aportion 342 ofSiN layer 334 is also etched away.Regions SiN layer beam 320 is cantilevered. Releasedportion 324 ofbeam 320 is separated fromSiN layers portion 325 ofbeam 320 remains firmly anchored inSiN layer 304. In this manner,beam 320 can function as part of a resonator or a support beam in a MEMS relay, for example. - While not described herein, various CMOS transistors may also be fabricated on
wafer 300 using known or later developed integrated circuit fabrication techniques. Upon completion,wafer 300 is sawn, or otherwise separated, into individual chips, also known as die. The separate die are then attached to a lead frame and encapsulated using a known or later developed IC packaging technique, such as molding with a mold compound, to provide a packaged MEMS device integrated with CMOS circuitry. -
FIG. 4A is a top sectional view andFIG. 4B is a cross sectional view of a portion of another example CMOS integrated circuit chip that includes aMEMS device 400 with abeam 420 formed in a layer(s) 404, 434 of silicon nitride. In this example,beam 420 is fabricated with a matrix of vias and troughs, as indicated in general at 427, etched through aportion 424 ofbeam 420. The matrix of vias andtroughs 427 result in a matrix of interconnectedmetallic members 427 withinterstitial space 426 distributed throughoutbeam portion 424. Initially,interstitial space 426 will be filled with SiN from SiN remaining fromSiN layer 404. In other words, interconnectedmetallic members 427 ofbeam portion 424 resemble a waffle pattern. -
MEMS device 400 is fabricated in a similar manner as shown inFIGS. 3A-3F with the added steps of fabricatingvias 426 andtroughs 427. Referring toFIG. 4B , during the plasma etch process described inFIG. 3F , a wafer on whichMEMS device 400 is fabricated is exposed to a carbon tetrafluoride plus oxygen (CF4+O2)plasma 450, 451 throughopenings 438, 439 to provide a strong etch rate forSiN layers etch stop layer 403 onsubstrate 402 and SiO2 topdielectric layer 436. In another example, it is possible to replace or add other dielectrics like Al2O3 in order to further reduce the etching of the dielectric. In addition, it is possible to use metals that are not strongly attacked by the SiN undercut etch process above or below the MEMS beam as long as SiN is above and below these new structural layers. In this manner, undercutregion 440 andcontact region 443 are formed. Aportion 441 of undercutregion 440 extends across the bottom of aportion 424 ofbeam 420 and up the sides of theportion 424 ofbeam 420. A portion 442 ofSiN layer 434 is also etched away so thatportion 424 ofbeam 420 is separated fromSiN layers portion 425 ofbeam 420 remains firmly anchored inSiN layer 404. In this manner,beam 420 can function as a MEMS relay. - In this case,
plasma etch 450 removes SiN frominterstitial space 426 and then diffuses throughinterstitial space 426 to form portions of undercutregion 441. In this manner, an extensiveundercut region 441 can be formed under beams that are larger than a what can be formed under a solid beam, such as beam 120 (FIG. 1 ). -
FIG. 5 is a cross sectional view of a portion of another example CMOS integrated circuit chip that includes aMEMS device 500 with a releasedmechanical structure 520 formed in a layer(s) ofsilicon nitride silicon substrate 502 In this example theW VIA feature 520, surrounded by CVD TiN 505 on all sides but the top, originally embedded in SiN lands on a patterned metal feature. In this example, the bottom patterned feature contains layer of 560 of iridium (Ir) is positioned on the bottom ofbeam 520 during the fabrication process. The bottom patterned feature can be made of any material dielectric or metallic that is not strongly attacked by the SiN undercut etch. In this example, the bottom layer is composed of a layer of 561 TiAlN on top ofIr 560. In this example theIr 560 is on the bottom of a movingMEMS beam 520. This might function as a top contact for a bottom layer that is not shown in this figure to create a relay where the relay is closed when the beam is bent down to make electrical connection to a bottom electrode that is not moving in this example. As discussed earlier, the W is protected from the SiN undercut etch process bySiO2 536 on top of the W. The CVD TiN can protect the W on the sides and on the bottom if necessary. In this case this protective top layer is patterned and etched prior to the SiN undercut process. - In this example, undercut
region 540 is fabricated using a plasma of carbon, fluorine, and oxygen (CxFy+O2) to provide selective gas removal of the SiN layers 503, 534 through an opening indielectric SiO2 layer 536 and yet not attack theIr layer 560 or etch stopSiO2 layer 503. -
FIG. 6 is an example packagedMEMS device 600. In this example, anintegrated circuit chip 671 is fabricated using a known or later developed CMOS fabrication technique.CMOS circuitry 672 is formed inIC 671 and includes CMOS transistors, passive devices, and interconnecting conductors. One ormore MEMS device 673 is formed inIC 671.MEMS device 673 may be similar to any of devices 100 (FIG. 1 ), 400 (FIGS. 4A, 4B ), 500 (FIG. 5 ) or other MEMS device fabricated within a SiN layer using a plasma etch process as described in more detail hereinabove. -
IC 671 is attached to alead frame 670 that includescontacts 674.Bond wires 675 connect bond pads onIC 671 tocontacts 674 using a known or later developed wire bonding technique. - A
mold compound 676 encapsulatesIC 671 using a known or later developed encapsulation technique. In this example, completedMEMS device 600 is packaged as a surface mount device. - In described examples, CVD tungsten protected by CVD TiN on 3 sides is used to form a beam structure within SiN. The top side can be protected by another patterned and etched layer or by a self-aligned process like recess the W followed by barrier metal like TiN and more CMP. In other examples, physical vapor deposition (PVD) of titanium, Ta, TiW, TiN, TaN may be used to form a beam structure within SiN, for example. In each case, the use of a carbon, fluorine, and oxygen plasma to undercut the SiN has less impact on other materials. SiN is stronger and has a higher thermal conductivity than SiO2.
- SiN undercut etch results in a clean surface where residual carbon or fluorine can be removed using plasma or vapor cleaning process with H2, H2O, O2, N2, NH3, NO, etc.
- In described examples, W is used for the low creep material. However, there are other low creep materials, examples of which are included in Table 1. All the materials in Table 1 have extremely high melting temperatures above 1500 C, with most of them having a melting temperature above 2000 C. Materials that are typically used in semiconductor processing that qualify as low creep materials are C, Ta, Mo, Ir, Ru, Ti, and Pd. In addition, there are compounds like TiN or TaN that also qualify as high melting point and low creep materials. Alloys including the commonly used W alloys like TiW and NiW are also high melting temperature and low creep. With a few exceptions, most of the materials listed in Table Tare not typically used in CMOS processing and therefore do not have a well-established materials processing infrastructure of deposition, etch and clean. Most of these materials may be deposited by sputter deposition and hence need to be patterned by pattern and etch process and not the damascene process discussed in described examples. Some of these materials will be etched by an SiN undercut etch process and therefore will need to be protected. This can be done using protective layers at the top and bottom of the stack such as Ta or even a thin layer of SiO2, TiN, Al or AlOx. If necessary, the sides can also be protected by depositing the protective material (CVD TiN, AlOx) followed by etch back process to remove materials on the planar exposed surfaces. One advantage of an etch process to create the beam instead of the damascene process is that a solid beam can be created.
-
TABLE 1 Example Low Creep Materials Atomic Melting point Material number 1825 K 1552° C. 2826° F. Palladium Pd 46 1933 K 1660° C. 3020° F. Titanium Ti 22 1936 K 1663° C. 3025° F. Lutetium Lu 71 2028 K 1755° C. 3191° F. Thorium Th 90 2045 K 1772° C. 3222° F. Platinum Pt 78 2113 K 1600° C. 2912° F. Protactinium Pa 91 2125 K 1852° C. 3366° F. Zirconium Zr 40 2130 K 1857° C. 3375° F. Chromium Cr 24 2175 K 1902° C. 3456° F. Vanadium V 23 2239 K 1966° C. 3571° F. Rhodium Rh 45 2473 K 2200° C. 3992° F. Technetium Tc 43 2500 K 2227° C. 4041° F. Hafnium HF 72 2523 K 2250° C. 4082° F. Ruthenium Ru 44 2573 K 2300° C. 4172° F. Boron B 5 2716 K 2443° C. 4429° F. Iridium Ir 77 2741 K 2468° C. 4474° F. Niobium Nb 41 2890 K 2617° C. 4743° F. Molybdenum Mo 42 3269 K 2996° C. 5425° F. Tantalum Ta 73 3300 K 3027° C. 5481° F. Osmium Os 76 3453 K 3180° C. 5756° F. Rhenium Re 75 3680 K 3407° C. 6165° F. Tungsten W 74 3773 K 3500° C. 6332° F. Carbon C 6 - In described examples, a simple beam structure that can be used as a relay is described. In described examples, a beam that has a generally rectangular shape is described. In other examples, more complex structures may be formed within SiN using the plasma etch process described herein. These structures can be used in an extremely wide variety of different MEMS structures. A wide variety of materials that are compatible with the plasma etch undercut process can be used to create many types of possible devices. These can be simple structures to create actuators using electrostatic, magnetic, piezoelectric, thermal. The high temperature metals such as Pt, Ir, W, Ru, Mo, Ti can be used to create high temperature heaters which have numerous applications such as gas flow sensors, IR sources. MEMS structures with these can be used to create resonators, IR detectors, heat detectors. Electrical structures such as relays or RF switches with reliable contact materials are possible. Variable capacitor devices can be made using a flexible beam as described herein.
- In described examples, a portion of a beam is released from a SiN layer, while another portion remains embedded in the SiN layer. In other examples, a released mechanical structure that has no portion remaining in the SiN layer may be fabricated. In some examples, a released mechanical structure may be supported by a torsion bar or similar support mechanism that is attached to the SiN layer. As used herein, the term “mechanical structure” refers to both fully and partially released structures of various shapes and sizes.
- In described examples, a cantilevered beam is positioned within a cavity in a SiN layer. In other examples, the SiN layer may be configured so that it does not completely enclose the cantilevered mechanical structure. For example, there may not be a top layer over the mechanical structure. In another example, a large portion of the SiN layer may be removed, in which case the cantilevered mechanical structure may project from an edge of the SiN layer into essentially open space.
- In described examples, the finished packaged devices are surface mount devices with multiple contacts on a bottom side of the package. However, in other examples, the IC package may have any number of known or later developed configurations, and may have various form(s), material(s), shape(s), dimension(s), number(s) of contacts, shape(s) of contacts, etc. Moreover, the MEMS resonator(s) and/or any other components may be packaged, mounted, etc. in the IC package in various configurations. Other examples of IC packages include a wafer-level package and a die-level package.
- Many devices are encapsulated with an epoxy plastic that adequately protects the semiconductor devices and has mechanical strength to support the leads and handling of the package. Some integrated circuits have no-lead packages, such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) devices that physically and electrically couple integrated circuits to printed circuit boards. Flat no-lead devices, also known as micro lead frame (MLF) and small outline no-leads (SON) devices, are based on a surface-mount technology that connects integrated circuits to the surfaces of printed circuit boards without through-holes in the printed circuit boards. Perimeter lands on the package provide electrical coupling to the printed circuit board. Another example may include packages that are entirely encased in mold compound, such as a dual inline package (DIP).
- In this description, the term “couple” and derivatives thereof mean an indirect, direct, optical, and/or wireless electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through an optical electrical connection, and/or through a wireless electrical connection.
- Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.
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US20140064904A1 (en) * | 2012-09-06 | 2014-03-06 | Andreas Bibl | Compliant micro device transfer head with integrated electrode leads |
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